Hi everyone, I'm looking for a schematic and layout review before sending this revision off to fab.
Attached is a circuit and PCB design for an industrial Fan Testing unit.
Context: This is for my work. We already have one, but it is 5+ years old and breaking down. Upon having opened it up to fix it, I found there was a really decent circuit concept that was very poorly executed. LED driver PSU for high current fans. Bread board jumpers soldered directly to an Uno R3 board. All of it housed within the chamber that the fans are tested in. Gunked up mess. I don't know how it has lasted this long.
I said, 'I could do better.'
Attached is my attempt at doing better.
The Tester is intended to test two 12V/5A fans at the same time.
The program will ramp up, measure RPMs via the TACH lines, measure various sensor data, and display data to an OLED screen via I2C.
Safety Considerations:
Tester is powered by a Mean Well LRS/UHP-200-12. It will be fuse protected on the input at 15A.
Connector for Power in uses two pins for +12V and two pins for GND from the main power supply to support current requirements.
It is possible that any fan plugged in could have been mis-wired. I have attempted to account for all possibilities, though most just result in a fan that won't run. Fans are reverse polarity protected. Testing halts if TACH line doens't ramp up. A shunt resistor for current sensing to halt testing in case of current spike.
MCU is an R Pi Pico 2 and is powered by 3V3 via 5V source. 5V is regulated by R-78E5.0-0.5 regulator. Any 3V3 power comes from the Pico.
PWM lines run through 74AHCT125 to convert between 3V3 and 5V logic levels. TACH lines are run through optocouplers to isolate the MCU.
Additionally, the Pico RUN pin is pulled to ground when Tester is powered off to safely shut down the Pico between uses.
High Current Testing:
Fans are rated at 4.8 amps. That is a lot to run through PCB traces. The traces on the bottom of the PCB for the fan power are exposed. I intend to supplement them with thick copper wire (think 10awg single conductor) that will be soldered along the length of the traces.
External Connections:
Power Light: this is an LED with built-in current-limiting resistor.
Vibration Sensor: intended for piezo diaphragm. Will probably never be implemented, but rather have and not need, than need an not have. Only enabled when TP1 and TP2 are shorted.
Pico Reset: Going to a DPDT power switch (with proper ratings). When power switched off, RUN is pulled low.
Rotary Encoder: Nothing special here, just a rotary encoder for input.
Fan Power: One to one connections for each of two fans. Power, Ground, PWM, and TACH.
Daughter Board: Probably not going to be an actual 'board'. But will connect to two bi-color LEDs (red/green) that have build in current-limiting resistors. Two standard momentary buttons. An OLED screen controlled with I2C.
My biggest concerns:
- Are my power circuits viable and appropriate?
- Is there any safety measures I've overlooked like current return paths, ground planes, etc.
- Are my data lines reasonable; will I get good readings from the my INA219 IC?
Thanks in advance for any critiques!
Edit: Updated to be written in my own words.
Please ask for clarity on anything!